Graphene is a semiconductor material having a very high charge carrier mobility (e.g. in the range from about 50,000 to about 200,000 cm2/Vs on an insulating substrate). However, monolayer graphene has no bandgap so that a transistor based on graphene cannot be completely switched off. One possibility to generate a bandgap is to provide a two-layer graphene, to which an electric field may be applied perpendicular to the graphene layer direction.
In a conventional embodiment of a transistor based on graphene as described above, the electric field is generated by a further electrode (bottom gate) provided next to the actual gate electrode (top gate) of the transistor. This design requires a correspondingly complex expense for this further electrode. At the same time, the leakage current between the transistor channel and this further electrode results in a corresponding power loss.
Furthermore, graphene is a semiconductor material which is slightly p-type conductive due to interactions with the substrate and adsorbates. The production of n-type conductive graphene or stronger p-type conductive graphene, which is provided for the implementation of pn-junctions, may be realized by corresponding doping.
Conventionally, the doping is carried out by adsorption of dopants which induce an electric field in the graphene. In this case, it may be difficult that these dopants are not stable in particular at an increased temperature during the component manufacturing process. Thus, the pn-junction may degrade. A further possibility is the direct incorporation of the dopants into the graphene, wherein, however, the charge carrier mobility within the graphene layer may degrade due to the lattice imperfection of the sp2 carbon lattice.